1. Field of the Invention
The present invention relates to a hydraulic dynamic pressure bearing motor for a thin HDD device, and particularly to a hydraulic dynamic pressure bearing motor suited for a driving source of a body of rotation or a small and thin HDD device for a magnetic disk with a diameter of 2.5 in. or less.
2. Description of the Related Art
FIG. 1 is a cross sectional view showing a hydraulic dynamic pressure bearing motor in the related art disclosed in JP-A-8-321131. Namely, in FIG. 1, there is disclosed a hydraulic dynamic pressure bearing motor and an HDD device employing the hydraulic dynamic pressure bearing motor as a driving source. The hydraulic dynamic pressure bearing motor comprises a rotor, a stator, and a hydraulic dynamic pressure bearing supporting the rotor on the stator. The rotor includes a rotor magnet 12 and has a rotary shaft 15 and a hub 16 fixed to the rotary shaft 15 at one end thereof with axes of the rotary shaft 15 and the hub 16 being on the same axis. On the hub 16, there are mounted one or a plurality of magnetic disks 1 in stacked relation and spaced-apart from one another by spacers 13. The stator includes a base plate 7 and a stator coil 11 producing a turning force by an interactive electromagnetic action with the rotor magnet 12. Also shown in FIG. 1 are a cover 8, a flange 9, a bearing 10, a seal 14, a clamp 17, and a housing 19 of the hydraulic dynamic pressure bearing motor.
The hydraulic dynamic pressure bearing used in the above hydraulic dynamic pressure bearing motor in the related art comprises as bearing components the rotary shaft 15, a sleeve (bearing) 10 into which the rotary shaft is rotatably inserted, and an upper thrust bearing member 18 fixed on the rotary shaft 15, and lubricating fluid filling minute clearances formed by the above bearing components. Of the minute clearances, a radial clearance between an outer peripheral surface of the rotary shaft 15 and an inner peripheral surface of the sleeve (bearing) 10 constitutes together with the outer peripheral surface of the rotary shaft 15 and the inner peripheral surface of the sleeve 10 a radial bearing section of the hydraulic dynamic pressure bearing. On one of the outer peripheral surface of the rotary shaft 15 and the inner peripheral surface of the sleeve (bearing) 10 constituting the radial bearing section, there are formed herringbone type radial dynamic pressure generating grooves. Moreover, on one of the bottom surface of the upper thrust bearing member 18 and the upper end face of the sleeve (bearing) 10, there are formed spirally grooved thrust dynamic pressure generating grooves.
In the hydraulic dynamic pressure bearing motor in the related art, as shown in FIG. 2. a clearance in the radial direction between the rotary shaft 15 and the sleeve (bearing) 10, i.e. a radial clearance xcex4 (xcexcm), is determined so that six times the clearance xcex4 does not exceed a value of (1/d)xc3x97xcex94, the product of a ratio (1/d) and a minimum clearance xcex94 in the axial direction between the magnetic disk and a head loading arm 6, where d is the radius of the magnetic disk (mm) l and l is the bearing length (mm) in the axial direction, respectively. Furthermore, in FIG. 2, W and S represent inclination and eccentricity of the magnetic disk 1 at the rim thereof, respectively.
By the foregoing construction as shown in FIG. 3, even when no bearing stiffness is provided for the hydraulic dynamic pressure bearing motor at rest, the magnetic disk 1 can be kept so as not to contact with a head supporting system such as a head loading arm 6. Stated otherwise, although the rotary shaft at rest is inclined within a range of the radial clearance xcex4 of the radial bearing section, the radial clearance xcex4 is determined so that the magnetic disk 1 never contacts with the head loading arm even with the maximum inclination of the rotary shaft. This has allowed an increase in the number of stacked magnetic disks to realize an HDD device with a large capacity.
Incidentally, in recent years, an HDD device has been highly regarded as the most excellent storage medium mounted in an information home appliance. This is due to evaluation of a number of superior features of the hydraulic dynamic pressure bearing to a rolling bearing, in particular to a feature of considerably softened noise. A large amount of dynamic image information to be processed in the information home appliance requires an HDD device in the information home appliance to be provided with a high storage density.
Accordingly, the applicant also has been engaged in, developing a compact and thin hydraulic dynamic pressure bearing motor used for a small size HDD device on which there are mounted magnetic disks with a diameter of 2.5 in. or less. The thinned hydraulic dynamic pressure bearing, however, caused the length of a bearing section to be shortened which determines the inclination of the rotary shaft. This resulted in a problem in which the relation disclosed in the above JP-A-8-321131 could not be satisfied. Namely, the relation could not satisfied in which six times the clearance xcex94 does not exceed a value of (1/d)xc3x97xcex94, the product of (1/d), a ratio of the bearing length l in the axial direction to the radius d of the magnetic disk l, and a minimum clearance xcex94 in the axial direction between the magnetic disk and a head loading arm. Hence, a structural problem occurred in which, when the rotary shaft at rest is inclined within a range of the radial clearance xcex94 of the radial bearing section, the magnetic disk 1 is brought to be in contact with the head loading arm to damage the disk or the head.
Accordingly, it is an object of the present invention to solve the above problem and to provide a compact and thin hydraulic dynamic pressure bearing motor used for an HDD device which is provided with a thin hydraulic dynamic pressure bearing being constituted by comprising a flanged rotary shaft having a shaft section and a flange section, a sleeve into which the flanged rotary shaft is rotatably inserted, and lubricating fluid filling minute clearances formed by bearing components including the above flanged rotary shaft and the sleeve, in which, even when no bearing stiffness is provided for the hydraulic dynamic pressure bearing motor at rest, the magnetic disk is made so as not to contact with a head supporting system such as a head loading arm.
In order to solve the above problem, in a compact and thin hydraulic dynamic pressure bearing motor used for an HDD device which motor is provided with a thin hydraulic dynamic pressure bearing being constituted by comprising a rotary shaft, a sleeve into which the rotary shaft is rotatably inserted, a thrust member fixed to the rotary shaft, and lubricating fluid filling minute clearances formed by those bearing components, a diameter of the thrust member and the minute clearance are determined so that the rotary shaft at rest is inclined within a range of the minute clearance without making the magnetic disk contact with a head and components constituting a head supporting system.
Namely, in order to solve the above problem, in a hydraulic dynamic pressure bearing motor comprising a rotor with a hub mounting a magnetic disk thereon being fixed to a rotary shaft at one end thereof with an axis of the hub and the axis of the rotary shaft being on the same axis, a stator generating a force for rotating the rotor by an interactive electromagnetic action between the rotor and the stator, and a hydraulic dynamic pressure bearing supporting the rotor on the stator, the hydraulic dynamic pressure bearing is employed which is constituted by comprising as prime bearing components a flanged rotary shaft having a shaft section and a flange section, and a sleeve into which the flanged rotary shaft is rotatably inserted, the bearing components forming between them a plurality of minute clearances comprising a radial clearance and a thrust clearance, the flanged rotary shaft that forms the radial clearance being provided with thereon radial dynamic pressure generating grooves, the flanged rotary shaft that forms the thrust clearance being provided with thereon thrust dynamic pressure generating grooves, and a plurality of the minute clearances being filled with lubricating fluid. A diameter of the flange section of the flanged rotary shaft and the thrust clearance are determined so that the flanged rotary shaft at rest is inclined within a range of the thrust clearance without making the magnetic disk contact with a head and components constituting a head supporting system.
More specifically, the thrust clearance c was determined as being equal to or less than a value for which a product md of a maximum vertical shift m at a rim of the magnetic disk and a diameter d of the flange section of the flanged rotary shaft is divided by 4r, four times a radius r of the magnetic disk.
Moreover, in the hydraulic dynamic pressure bearing motor according to the present invention, the hydraulic dynamic pressure bearing, in which the diameter of the flanged rotary shaft and the thrust clearance are determined as above, is a hydraulic dynamic pressure bearing in which the radial dynamic pressure generating grooves are formed on an outer peripheral surface of the flange section, and the thrust dynamic pressure generating grooves are formed on both of upper and lower radial surfaces of the flange section. Alternatively, in the hydraulic dynamic pressure bearing of the present invention, the radial dynamic pressure generating grooves are formed on an outer peripheral surface of the shaft section, and the thrust dynamic pressure generating grooves are formed on both of upper and lower radial surfaces of the flange section.